Lower boundary age of the Nanhua System and the Gucheng glacial stage: Evidence from SHRIMP? dating

Abstract

In the newly revised Regional Chronostratigraphic (Geochronologic) Scale of China, the original bipartite division of the Neoproterozoic is changed to tripartite division. The three “system”-rank chronostratigraphic units are in ascending order of the Qingbaikou, Nanhua and Sinian Systems. This report presents SHRIMP zircon U-Pb dating on volcanic tuffs from the candidate stratotype section of the Nanhua System at the Yangjiaping section that is geographically located in Hupingshan Town, Shimen County, Hunan Province. Tuff from the upper part of the Xieshuihe Formation (equivalent to the Liantuo Formation) in the Lower Nanhua Series yields a zircon U-Pb age of 758 ± 23 Ma, which may provide a constraint on the lower limit of the Gucheng glacial stage in the Nanhua System. Tuff from the Laoshanya Formation of its underlying Qingbaikou System (equivalent to the Banxi Group) gives a zircon U-Pb age of 809 ± 16 Ma. The sampling locality lies 12 m from the upper boundary of the Qingbaikou System. According to the sedimentation rate it is estimated that the upper boundary age is about 800 Ma. The present studies also provide a resolution to the long-standing problems concerning stratigraphic correlation of the Late Precambrian in South China whether the Liantuo Formation is equivalent to the Banxi Group or not.